1. Field of the Invention
The present invention relates to automatic telephone call redirecting service systems. More specifically, the invention relates to a media gateway, IP call connection controller, and automatic telephone call redirecting service system for redirecting an incoming call on an IP telephone to a forwarding destination telephone which has been registered beforehand in a network configuration that interconnects IP telephones and PSTN telephones.
2. Description of the Related Art
In conventional Public Switched Telephone Networks (PSTNs), a plurality of packet exchanges (packet switches) operate relationally through common-channel interoffice signaling and thereby provide high intelligent telephone services. One of the high intelligent services is, for example, automatic call redirecting that redirects an incoming call on a subscriber telephone to another telephone having been designated beforehand when the subscriber is away from where his or her telephone is.
The automatic call redirecting service is realized such a way that a called side exchange refers to a data base that indicates correspondence between a called telephone number and a forwarding destination telephone number and determines a forwarding destination telephone number, for example, as described in JP-A No. Hei 7-162529 (Related art 1). If a forwarding destination telephone is accommodated by another exchange, a call connection between a calling telephone and the forwarding destination telephone is established by-communicating control signals between the called-side exchange and the forwarding destination exchange via a common channel signaling network, for example, as presented in the Aug. 7, 2000 issue of the journal Nikkei Communications, p. 103, FIG. 3.
While the PSTNs provide the automatic call redirecting service by the above-described method, integration of PSTN and IP (Internet Protocol) network has lately been advancing and there is a need to extend various telephone services that have so far been provided by the PSTNs to IP telephones.
Connection between a PSTN and an IP network is realized by using a media gateway (MG) for performing conversion between Synchronous Transfer Mode (STM) voice signal data on the PSTN and IP voice packets, a signaling gateway (SG) for connecting a common channel signaling network and the IP network to transfer control signals, and a call agent (CA) for converting a common channel signal received by the signaling gateway SG into a control signal for the media gateway MG, such as, MGCP and the like, thereby to control the MG, for example, as presented in the Aug. 7, 2000 issue of the journal Nikkei Communications, “How to bridge PSTN and IP network for call routing? How is relation with IP telephone services?” (Related art 2), p. 105, FIG. 5.
According to this method, since the control signals can be communicated between the IP network and exchanges existing in the PSTN by accommodating common channel signals to both the signaling gateway SG and call agent CA, it is possible to provide services equivalent to that have been implemented on the existing PSTNs to IP telephones as well.
However, telephone network service providers desire to minimize the investment in infrastructures for call interconnection between PSTN and IP network. Therefore, a system configuration that requires a plurality of sets of expensive communications apparatuses such as media gateways MGs, signaling gateways SGs, and call agents CAs, as presented in related art 2, is not a favorable solution for communications service providers, because the cost of these apparatuses is high and they need to establish a new maintenance and operation system in the IP network side.
With regard to this problem, for example, in “Development and Provisioning of a Voice Service System” (related art 3) posted in “NTT Research and Development 2003 Review of Activities” on an NTT Corporation's web site/home page (http://www.ntt. co.jp/RD/OFIS/active/2003pdf/nw13.pdf), it is proposed to omit the signaling gateways SGs by communicating control signals in the IP telephone network side across the IP network instead of the common channel signaling network.